The present invention is based on a method and an arrangement for automatically controling the volume in an audio signal reproduction device.
Conventional radio receivers provide power amplifiers for amplifying an audio signal to be reproduce. The power amplifiers have an output where, in the event that a power amplifier is overdriven, a signal indicating an overdrive is present.
In prospectus xe2x80x9cProgramm 96/97xe2x80x9d of Robert Bosch GmbH car radios Berlin RCM 303 A and Atlanta RD 105 are described in which signal processing circuits in the form of digital signal processors (DSP) for automatic, disturbance-dependent volume control of the audio signals to be reproduced are provided. The reproduction volume of the audio signal is raised in a frequency-selective manner as a function of the intensity and the spectral distribution of the disturbing noise.
The arrangement according to the present invention has the advantage that the digital signal processor, which already exists in conventional radio receivers can also be used to prevent the power amplifier from being overdriven in addition to automatic volume control. In this manner, a separate microprocessor as well as a special electronically controllable volume control of the conventional radio receivers become dispensable. Moreover, the speed of response to an overdrive condition of the power amplifier increases considerably; in first tests a reduction of the response time by the factor 100 was achieved so that an overdrive condition is virtually inaudible.
In addition, the arrangement according to the present invention has the advantage that by selecting the values differently in the case of lowering and increasing the reproduction volume, as well as by delaying the increase of the reproduction volume after lowering the reproduction volume with the assistance of an inserted counter, control oscillations of the volume are no longer audible.
Furthermore, it is advantageous that, after a deactivation of the automatic volume control, the lowered reproduction volume is not raised to the originally preset value abruptly, but gradually using the time constant predefined by the method according to the present invention.
In the course of various measurements, it was ascertained that, in the event of overdrives conditions of the power amplifier, the lower-frequency portions of the audio signal cause these overdrive conditions in the majority of cases. Therefore, it is advantageous not to damp the entire audio signal in the event of an overdrive conditions but only the low-frequency portions of the audio signal are responsible for the overdrive, since such a frequency-selective volume lowering is less conspicuous than lowering the entire audio signal range.
Finally, it is regarded as advantageous to adapt the dynamic response of the volume control to the dynamics of the signal source or type of signal by selecting the volume and counter increments and decrements accordingly. Thus, for example, the audio signal played back from a compact disc (CD) has a considerably higher dynamic range than, for example, an audio signal emitted by a radio receiver.